Theoretical insight into methanol steam reforming on indium oxide with different coordination environments

Abstract

Indium oxide (In2O3) has demonstrated to be an effective non-noble metal catalyst for methanol steam reforming reaction (MSR). However, the reaction mechanism of MSR and crucial structure-activity relations determining the catalytic performance of In2O3 are still not fully understood yet. Using density functional theory (DFT) calculation, we systematically investigate the MSR process over a high-index In2O3(211) and a favoured catalytic cycle of MSR is determined. The results show that In2O3(211) possesses excellent dehydrogenation and oxidizing ability, on which CH3OH can readily adsorb on the In4c site and be easily activated by the reactive lattice oxygens, resulting in a total oxidation into CO2 rather than CO, while the H2 formation through surface H–H coupling limits the overall MSR activity because of the strong H adsorption on the two-coordinated lattice O (O2c). Our analyses show that the relatively inert three-coordinated lattice O (O3c) could play an important catalytic role. To uncover the influence of the local coordination of surface In atoms and lattice O on the catalytic activity, we evaluate the activity trend of several types of In2O3 surfaces including (211), (111), and (100) by examining the rate-limiting, which reveals the following activity order: (211)>(111)>(100). These findings provide an in-depth understanding on the MSR reaction mechanism over In2O3 catalysts and some basic structure-activity relations at the atomic scale, could facilitate the rational design of In2O3-based catalysts for MSR by controlling the local coordination environment of surface active sites.